No, I said 100 threads per inch!

The 1968 card design is infamously known as the "burlap" series. After the first series, the border design was altered to a finer "grain". This is best shown on the 2nd Series Checklist card.

In each series, Topps included the checklist for the current series, as well as for the next series. So, the 2nd Series Checklist was printed during the 1st series run...

... and with the redesigned border in the 2nd series run:


The back was the same for both versions: